1. Field of the Invention
The present invention relates to a perovskite type oxide material that can be used as a piezoelectric member, a piezoelectric element, a liquid discharge head and liquid discharge apparatus using the same, and a method of producing the perovskite type oxide material.
2. Description of the Related Art
A piezoelectric member has piezoelectric characteristics, that is, converting electric energy into mechanical energy, namely, converting electric energy into mechanical displacement, stress or vibration, and vice versa. A conventional piezoelectric element is formed by sandwiching a thin film of such a piezoelectric member between electrodes. When an electric field is applied to the piezoelectric member, the member causes displacement. In contrast, when the electric field is removed from the member, the state of displacement returns to the original state. A piezoelectric element uses such piezoelectric characteristics of the piezoelectric member and can be used in a motor, ultrasonic motor, transducer and actuator all requiring reciprocal movement. In addition, a piezoelectric element is frequently used in inkjet printers, communications, biotechnology, medical care and sensors such as an automobile acceleration sensor and a pressure sensor for measurement. With the advance of recent technology in the micro electromechanical system (MEMS), a piezoelectric element more reduced in size and more excellent in piezoelectric characteristics has been desired.
As a material for a piezoelectric member used in such a piezoelectric element, mention may be made of a PZT based material, which was found about 50 years ago. In an attempt to form a thin film of the PZT based material, which has a sintering temperature of 1100° C. or more, a sol-gel method, sputtering method, MBE method, PLD method and CVD method have been developed. However, the thin-film piezoelectric element formed of a PZT based material prepared by any one of the aforementioned methods has a problem in that a physical decomposition is likely to occur within the film or the film-interface. In particular, to obtain a high definition device reduced in size in the field of the MEMS, it has been desired to develop a material for a piezoelectric member further improved in piezoelectric characteristics and improved in uniformity of piezoelectric characteristics by suppressing variance in piezoelectric characteristics caused by miniaturization processing.
On the other hand, a ceramic material such as BaTiO3 and Pb (Zr, Ti)O3 has been used as a material for a condenser, since it has a high relative dielectric constant. To satisfy the requirement for reducing the size of a condenser, a ceramic material formed into a thin film has been desired. Unfortunately, when these ceramic materials, which have relative dielectric constants of about 1500, are processed into thin films, sintering failure and a defective structure at the film interface may occur. The resultant condenser formed of such a ceramic material may not be free from defective characteristics.
There are many reports on a piezoelectric material having improved piezoelectric characteristics and a method of producing such a material.
The specification of U.S. Pat. No. 6,793,843 discloses a piezoelectric electromagnetic device containing a rhombohedral perovskite structure compound, a tetragonal perovskite structure compound, and an orthorhombic perovskite structure compound.
Japanese Patent Application Laid-Open No. 2003-270602 discloses a single crystal perovskite oxide represented by ABO3, where the main component of reference symbol A is Pb and the main component of reference symbol B consists of at least three types of elements selected from the group consisting of Zn, Nb and Ti.
U.S. Patent Publication 2005-122005A1 discloses a method of forming a thin film of a perovskite type oxide using a single crystal material as a substrate.
However, the piezoelectric electromagnetic device disclosed in the specification of U.S. Pat. No. 6,793,843 has a problem. Since a mixture of perovskite structure compounds having different crystal systems is used, the piezoelectric characteristics of the device are improved but varied in sites. Obtaining a thin film having sufficiently uniform piezoelectric characteristics has remained unsolved.
On the other hand, a good ceramic material as disclosed in Japanese Patent Application Laid-Open No. 2003-270602 is not yet widely known. When a perovskite type oxide is formed into a thin film, it is very difficult to employ a sputtering method using a ceramic of a perovskite type oxide as a target.
U.S. Patent Publication No. 2005-122005A1 discloses an ion beam assist method. However, it is difficult to produce a perovskite type oxide having a large-area single crystal by this method. Furthermore, the method involves a high cost.